Security unit



FIG. 1 is a perspective view of the security unit design;

FIG. 2 is a front elevational view of the security unit, with the sideand rear views being the same as this view;

FIG. 3 is a top plan view of the design; and,

FIG. 4 a bottom plan view of the design.

The ornamental design for a security unit, as shown and described.